This invention relates to a triangulated roof structure which supports a roof for an underlying building, arena or stadium. More particularly, it relates to a roof structure formed of a plurality of tension members and compression members arranged in a triangulated manner for supporting a roof that projects in plan a closed non-circular curve.
In recent years, dome roofs have been constructed in a variety of manners. For example, some dome roofs are constructed wherein the roof is supported only by rigid structural members forming the dome without the use of interior columns or beams. Such structures, however, exhibit high aspect ratios, that is, the ratio of surface area to delineated plan area, in order to provide sufficiently low membrane stress. Other roof structures have been constructed wherein a lightweight membrane is supported by air pressure. These structures, while exhibiting low aspect ratios, suffer from numerous disadvantages. The primary disadvantage involves the reliance on a mechanical device, such as a blower, for structural stability. A breakdown in such a mechanical device results in deflations, a common problem for air-supported roofs. In addition, these air-supported roofs require an airtight underlying structure.
Other structures have been built using the principles of catenary suspension typically associated with the construction of suspension bridges. These structures often achieve the low aspect ratio of air-supported roof structures without the detrimental reliance on mechanical devices for structural stability. For example, U.S. Pat. No. 3,139,957 to Fuller illustrates structures in which a series of box frames of polygonal, cylindrical or other forms, of progressively varying sizes are arranged in a concentric array at sequentially different heights above a common plane of reference. These frames are also arranged in vertical overlapping spaced relation to one another to achieve incremental increases or decreases in altitude. Tension elements in the form of flexible cables or wires extend between and are secured to adjacent pairs of box frames in the series, which suspend and anchor the box frames to one another.
Specifically, each frame includes upper chord members and lower chord members which form polygons defining the upper and lower peripheries of the respective frames. Each frame also includes vertical compression columns which extend between the vertices of the polygon formed by the upper chord members and the corresponding vertices of the polygon formed by the lower chord members. A first pair of tension members are supplied which extend downwardly, in a criss-crossing manner, from their point of securement at two adjacent upper vertices of a lower frame to two corresponding adjacent lower vertices of an upper frame whereby successive frames in the series are suspended from one another. These tension members criss-cross when viewed in plan. A second pair of tension members are supplied which extend upwardly, in a criss-crossing manner, from their points of securement at two adjacent lower vertices of the lower frame of the pair to two corresponding adjacent upper vertices of the upper frame in the pair, whereby successive frames in the series are anchored down to one another. These tension elements also criss-cross when viewed in plan. Also, these two pairs of tension members, when viewed in elevation, also criss-cross.
In addition, two other pairs of tension members are supplied which are disposed in radial planes containing the central axis of the structure. The first pair of tension members extend downwardly from their point of securement at two adjacent upper vertices of the lower frame to two radially aligned lower vertices of an upper frame. The second pair of tension members extend upwardly from their points of securement at two adjacent lower vertices of the lower frame to two radially aligned upper vertices of the upper frame. These two sets of tension members criss-cross when viewed in elevation.
The Fuller structures while applicable to a wide range of building shapes, are unnecessarily complicated. Fuller requires a plurality of criss-crossing cables, and consequently, requires complicated attachment structures to accommodate the number of cables arriving at any particular attachment point. Also, due to the number of criss-crossing cables, which serve to suspend, anchor, buttress, resist torque, and resist counter-torquing of the frame, the Fuller structures are unduly redundant.
Further, although the roof structures described in the Fuller patent recognize the tremendous savings of constructing a building using the tensile strength of materials, the use of polygonal frames described in this reference and the number of tension members used to interconnect the series of frames to one another, provide serious drawbacks. The most serious drawback involves the problems encountered when the disclosure of Fuller is applied to structures having a non-circular perimeter. In particular, due to the concentric relation of the frames to one another, the angular relationship of anchoring cables and suspension cables to one another varies at successive frames and may also vary around the perimeter. Therefore, different attachment configurations must be designed for all of the vertices of each of the frames. This significantly increases fabrication costs and construction time.
Another example of a structure using catenary principles is the circular cable truss dome illustrated in U.S. Pat. No. 4,736,553 to Geiger. This truss dome, which is not triangulated, is constructed from a plurality of radially oriented support members. The support members include, in a vertical plane, at least one upper tensioned member forming a top chord, at least one diagonal tensioned member which extends inwardly and downwardly from the upper tensioned member and at least one vertical rigid strut in compression, which is attached at its upper end to the upper tensioned member and attached at its lower end to the diagonal tensioned member. In this arrangement, the tensioned members form two adjacent sides of a triangle while the compression member forms the third side. At least one horizontal tensioned hoop concentric with the outer compression ring is also provided. The tensioned hoop is affixed to the lower end of the compression member.
The radially oriented support members are attached at an outer edge to a continuous compression ring which delineates the area to be covered by the dome. At an inner end, the support members are attached to a horizontal inner tension ring. A flexible membrane is placed on top of the support members to form a roof for the delineated area. In addition, a plurality of valley cables are positioned on top of the flexible membrane, between adjacent support members, which extend between the compression ring and the inner tension ring to maintain the flexible membrane in tension.
This structure, however, does not use triangulated construction. As a result, the structure lacks a degree of lateral stability at the top radial chord of the dome and therefore relies on the flexible membrane for stiffness. Furthermore, due to the radial arrangement of the support members, this structure is only appropriate for use in circular stadiums. Most stadiums or arenas are, however, non-circular.
Roof structures have been developed to support a roof for such non-circular buildings. For example, U.S. Pat. No. 3,841,038 to Geiger relates to a non-circular roof structure which defines an enclosed building space, including a ring which projects in plan substantially to a closed curve having major and minor axes and a plurality of skewed axes of symmetry. In this roof structure, a plurality of sets of rigid arches are connected to the ring to form the roof, with the arches of at least two sets respectively extending in plan substantially parallel to a separate one of the skewed axes of symmetry of the closed curve, and the arches of another set extending in plan substantially parallel to the major or minor axis of the closed curve. These arches impose a funicular load on the ring and support a roof deck structure to form a domed surface.
This structure, while applicable to non-circular structures is unnecessarily complicated, requiring at some points the intersection of up to six arches. This causes extremely complicated attachments at these intersections. Also, this structure is constructed with rigid arches and, therefore, does not efficiently use the tensile strength of building materials and may also result in a roof structure having a high aspect ratio.
Because of the drawbacks highlighted above, none of these prior art roof structures efficiently utilize a triangulated arrangement of tension members and compression members to construct a roof adaptable to a variety of non-circular underlying arenas.